1. Field of the Invention
The present invention relates generally to a power and/or energy management system and, more particularly, to a system capable of monitoring the power and/or energy being consumed by a load and reducing the power and/or energy being consumed in order to stay below a predetermined value.
2. Related Art
Energy management systems capable of turning connected loads on and off to maintain the total connected power consumption below a predetermined maximum value are well known.
U.S. Pat. No. 5,196,982 to Landsberg et al. and assigned to The Fleming Group discloses a method and system incorporating an integral power consumption monitor-circuit breaker panel for industrial or commercial buildings and facilities. The power consumption monitor-circuit breaker panel not only protects each end use within the building against harmful overloads, but also monitors peak power demands of each end use. Electrical current, voltage and phase information is provided by each monitor-breaker. This information is then fed to a processing circuit that provides a power consumption value. The power consumption value is then fed to a recording device to provide a power consumption history for each end use. Each monitor-breaker is identified by its end use, as for example, by color coding. The monitor device of each circuit breaker is designed to provide a voltage that is proportional to the circuit load. Two methods may be used to provide such a voltage signal: a) the voltage signal can be developed across a built-in shunt in each circuit breaker; and b) a proportional voltage can be obtained by use of a circuit breaker with a built-in Hall effect device, wherein the product of the instantaneous current and voltage, along with the phase angle between them, provides the power measurement. The current and/or instantaneous power information can be sent to the recording device via a power line carrier, radio link, or optical fiber. The information can be integrated to provide either kW or kWxc2x7hr readings.
U.S. Pat. No. 4,819,180 to Heldman et al. and assigned to Dencor Energy Cost Control, Inc. discloses a method and system for regulating power delivered to different commercial or residential users in which each user has variable demands for power consumption, there being a power source from which power is transmitted by a utility to each user and a utility control signal which is transmitted from the utility to each user in order to modify the power consumed by each user, the method and system of the Heldman et al. reference being characterized by measuring the power consumption of each user over a selected real time interval, and modifying the power consumption by each user by an amount directly related to the power consumption measurement of each user over that time interval.
U.S. Pat. No. 4,977,515 to Rudden et al. discloses a plug in device, furnished by an electric power utility to a customer, which is installed by the customer between a wall outlet and an appliance, particularly a room air conditioner. The device contains a microprocessor that is programmable and controllable by the utility to determine the ON-OFF cycling of the appliance. The microprocessor, with the aid of sensors, records date and time of each instance that a programmed OFF interval is overridden through a manual input, and each instance of disconnection of the appliance from the device after the first connection. Also, the device is arranged on command to record the power being drawn by the attached appliance, either on a one time basis or on a scheduled interval over a predetermined time span. A remote transmitter is also provided as a source of customer I.D. and control signals for utility control of selected devices in use. Certain embodiments have a component that is installed by qualified personnel, hard wired into a control circuit, having a removable component removable either by service personnel or the customer for return to the utility to read out the contents of its memory as to its history of use. Similarly, the customer installed unit is returned or has a component returned for utility readout.
U.S. Pat. No. 4,075,699 to Schneider et al. and assigned to Lockheed Electronics Co., Inc. discloses an electrical power controlling/load shedding system that includes power consumption metering and meter interfacing circuitry for entering overall power consumption into a central processing unit (CPU). The CPU memory includes a data storage table characterizing each system electrical load under each of a hierarchy of operational levels, and circuitry is provided for turning local and remote loads on/off, responsive to CPU-issued commands. The digital computing apparatus operates on the meter supplied information and projects energy consumption over the monitoring interval. If power must be shed to obviate an excessive projected demand, loads are examined seriatim and selectively shed on a priority basis as required, depending upon the operational parameters and status characterizing each load for the then prevailing load level condition.
U.S. Pat. No. 5,572,438 to Elhers et al. and assigned to TECO Energy Management Services discloses an energy management and building automation system including a local area network or home automation data bus such as the CEBus. Each load is connected to the bus via a control module which may contain a circuit breaker to disconnect the load from the mains upon command or upon occurrence of a power outage. Current monitoring control modules measure load current and power monitor modules monitor power consumed by selected loads, both modules transmitting bus messages indicating load status and status changes. A first microcomputer preferably is external to the customer premises, adjacent the electric utility power meter. A second microcomputer preferably is inside the customer premises. The two microcomputers communicate with each other and with the various modules via the network/data bus. The first microcomputer communicates with the utility company via any appropriate communications link. The second microcomputer serves, in part, as an input/output terminal for the system, allowing the customer to set parameters and query the system as to power usage, displaying reports requested by the customer and messages transmitted by the utility company and by either microcomputer. The first microcomputer acts as a master controller and/or network server, communicating with the world outside the premises, as a communications gateway between voice, video and data services, and as the primary data collector and operator of the load control modules; the second microcomputer provides certain backup functions. The utility company can access selected utilization data and control at least some loads via messages to the first microcomputer.
Unfortunately, the preceding patents disclose systems which completely disconnect one or more selected loads (reduce output power to zero) when the power usage exceeds a predetermined maximum. None of these systems have the ability to reduce the power/energy to the load without completely disconnecting the load. Accordingly there is a need in the art for a new power/energy management system capable of monitoring output power/energy draw and varying available output power/energy to maintain desirable output power/energy draw.
In order to overcome the disadvantages of the prior art, a circuit for controlling power drawn from a source of utility power and delivered to a load according to the present invention includes:
a power monitoring circuit operable to produce a sense signal indicative of an amount of output power drawn by the load;
a control circuit operable to receive the sense signal from the power monitoring circuit and produce a control signal indicative of whether the amount of power drawn from the source by the load has exceeded a threshold; and
an output circuit operable to receive input power from the source and deliver the output power to the load, the output circuit reducing the output power when the control signal indicates that the threshold has been exceeded.